The present invention relates to a load driving device and a load driving method, and more particularly to a load driving circuit and a load driving method, which drive an inductive load with the use of a power transistor with a vertical structure, having an output controlled by a transistor with a horizontal structure.
As a load driving apparatus for use in a vehicle, a low side switch is used to drive an inductive load such as a solenoid coil or a relay switch. A switch provided in the low side switch is connected to a low side, and the load is connected to a high side. This low side switch may be provided with a disconnection detection circuit for detecting a disconnection of the load, an overcurrent protection circuit for protecting the switch or the load from an overcurrent generated when the load connection is in an abnormal state such as a short circuit, or an over-temperature protection circuit.
A power MOSFET (metal oxide semiconductor field effect transistor) with a vertical structure, which can reduce a power loss is used in a switch transistor provided in the low side switch. A MOSFET or a polysilicon resistor with a horizontal structure is used in a control circuit for the disconnection detection circuit or the protection circuit.
The low side switch of this type is disclosed by, for example, “Intelligent Power MOSFET”, Fuji Times, vol. 81, No. 6, 2008 (Non-patent document 1), and Japanese Unexamined Patent Publication No. 2000-12853 (Patent document 1).